1. Field of the Invention
This invention relates to gas generators, or inflators, using pyrotechnic gas generant for inflating air bags which are part of a vehicle occupant restraint system.
2. Description of Prior Art
Gas bags, which are more commonly referred to as air bags, are mounted within vehicles in positions to deploy in the event of a crash and to cushion an occupant from the effects of the crash. It is well known in the art to inflate air bags by gas generators using a combustible solid gas generant charge.
A typical gas generator for a passenger side air bag includes a cylindrical housing having openings therein for release of gas, a gas generant charge deployed along the interior length of the housing in pellet or wafer form, and a cooling and filtering structure surrounding the combustible gas generant charge in order to filter out hot or burning particles and cool the gas produced by the gas generant charge. Ignition of the gas generant charge is achieved by an igniter tube extending through the gas generant charge along the axis of the charge and the housing. The tube typically contains rapid detonation cord, or fuse, and igniter powder. An electric initiator and charge, or squib, is mounted at one end of the housing and lights the fuse. The fuse in turn sets off the igniter powder, which bursts the igniter tube and lights the gas generant charge.
Although it is a requirement that a gas generator produce gas very quickly so that the air bag deploys in time to provide occupant protection, there are also disadvantages in deploying the air bag too quickly. In particular, an overly rapid deployment of the air bag can injure an out-of-position occupant, especially a child. Thus, it is preferable that the initial deployment of the air bag be somewhat retarded, in order to avoid such an injury.
Most proposals for controlling the rate of initial gas generation have involved dividing the inflators into two stages. This is sometimes accomplished by dividing the single inflator housing into two chambers or compartments, each of which contain combustible gas generant material and providing a delay between ignition in the two chambers.
All of the foregoing has led to more complexity and cost in the manufacture of gas generators for air bags. As such gas generators are more widely used in vehicles, there is a need for more economical construction and ease of assembly, with due regard for controlled delivery of inflation gases to protect an out-of-position occupant.